Thursday is a sacred holiday. Oct. 3 is Mean Girls Day. Anyone who hasn’t seen the 2004 high school comedy might be wondering why it’s such a well-known day.

“Mean Girls,” written by Tina Fey, follows Cady (Lindsay Lohan) as she adjusts from being homeschooled in Africa to going to a regular American high school. She quickly develops a crush on Aaron Samuels (Jonathan Bennett) and starts tracking all the nonchalant things he says to her.

“On Oct. 3, he asked me what day it was,” Cady says in a voiceover.

It is a simple line, but it was quite memorable. In the years since the movie came out, the gif and meme became widely shared. Now, Oct. 3 is more well-known than the movie’s actual anniversary (April 30, 2004).

So what is the original “Mean Girls” cast up to now? They're celebrating Oct. 3 by asking fans to give to charity with the hashtag #MeanGirlsDoGood.

Jonathan Bennett teamed up with the original cast to create a video asking fans to donate to Thirst Project to help fund a well in Uganda. Lindsay Lohan, Lizzy Caplan, Lacey Chabert, Amanda Seyfried, Rajiv Surendra, Jan Caruana, Stefanie Drummond and Daniel Franzese all They ask that fans chip in $3 each.

“So we all know Cady was from Africa, but this year, we want to help building a well in Uganda,” Lohan says.

“Eight thousand dollars is all it costs to build a well for an entire village,” Bennett explains.

Fans can donate to the Mean Girls Do Good campaign on Thirst.

Elsewhere, Tina Fey is hosting an official “Mean Girls” watch party with Busy Philipps on Facebook to celebrate the 15th anniversary of the film. The event will be streamed on the “Mean Girls” Broadway Facebook page.

The Tony-nominated Broadway musical, also penned by Fey, launched in 2015 and is still going strong. There’s even a touring production so Regina and the Plastics can be seen around the country.

To celebrate Mean Girls Day, there’s a special ticket offer. Fans who use code OCT3 between Oct. 3 and Oct. 7 will unlock special ticket offers on select performances for both the Broadway and touring productions.

Mean Girls movie
A promotional photo for 2004's "Mean Girls." From left: Lacey Chabert, Rachel McAdams, Lindsay Lohan, Amanda Seyfried. Paramount Pictures